如何避免循环引用 asp.net core mvc [HttpPost("add-recipe")] web api

Question

我的项目是 Application with Recipes (cooking) .NET Core 5.0

我在添加新配方 (HttpPost) web api 时遇到问题

关于邮递员，我的回答是：

“检测到可能的对象循环。这可能是由于循环或对象深度大于最大允许深度 32。考虑在 JsonSerializerOptions 上使用 ReferenceHandler.Preserve 以支持循环。”

当我创建一个新配方时，它应该使用 recipeToCreateDto 而不是 Recipe - 它包含所有属性（循环引用）

您能帮我如何使它正常工作吗？如何映射等。

https://i.postimg.cc/Mphv7zRH/screen.png

我正在使用 AutoMapper 来映射类和存储库模式。

public class AppUser
    {
        public int Id { get; set; }
        public string UserName { get; set; }
        public ICollection<Recipe> Recipes {get; set;} 
    }
}

用户有很多食谱。

 public class Recipe
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public AppUser AppUser { get; set; }
        public int AppUserId { get; set; }
    }

数据传输对象

public class RecipeForCreateDto
    {
        [Required]
        [StringLength(50, MinimumLength = 3, ErrorMessage = "You must specify name between 3 and 50 characters")]
        public string Name { get; set; }
        public int AppUserId { get; set; }
        public int AuthorId { get; set; }
    }

在我的 AutoMapperProfiles.cs 中

public class AutoMapperProfiles : Profile
    {
        public AutoMapperProfiles()
        {
        CreateMap<RecipeForCreateDto, Recipe>();
        }

配方界面

  public interface IRecipeRepository
    {
      Task<Recipe> AddNewRecipe(Recipe recipe);
    }

    public class RecipeRepository : IRecipeRepository
    {
        private readonly DataContext _context;
        private readonly IMapper _autoMapper;
        public RecipeRepository(DataContext context, IMapper autoMapper)
        {
            _autoMapper = autoMapper;
            _context = context;
        }

 public async Task<Recipe> AddNewRecipe(Recipe recipe)
        {
            await _context.Recipes.AddAsync(recipe);
            await _context.SaveChangesAsync();

            return recipe;
        }

}

用户控制器：

User.GetUsername() 是获取用户名的静态方法。

[HttpPost("add-recipe")]
        public async Task<ActionResult> AddNewRecipe(RecipeForCreateDto recipeForCreateDto)
        {
            var userFromRepo = await _userRepository.GetUserByUsernameAsync(User.GetUsername());

            recipeForCreateDto.Name = recipeForCreateDto.Name.ToLower();

            if (await _recipeRepository.RecipeExists(recipeForCreateDto.Name))
                return BadRequest("Recipe with that name already exists!");

            var recipeToCreate = _autoMapper.Map<Recipe>(recipeForCreateDto);

            recipeToCreate.AppUserId = userFromRepo.Id;


            var createdRecipe = await _recipeRepository.AddNewRecipe(recipeToCreate); // here is problem 

            var recipeToReturn = _autoMapper.Map<RecipeForDetailDto>(createdRecipe);


            return CreatedAtRoute("GetRecipe", new { controller = "Recipes", id = createdRecipe.Id }, recipeToReturn);
        }

Answer 1

[HttpPost("{recipeForCreateDto}")]
public async Task < ActionResult > AddNewRecipe([FromBody] RecipeForCreateDto recipeForCreateDto) {
    var userFromRepo = await _userRepository.GetUserByUsernameAsync(User.GetUsername());

    recipeForCreateDto.Name = recipeForCreateDto.Name.ToLower();

    if (await _recipeRepository.RecipeExists(recipeForCreateDto.Name)) return BadRequest("Recipe with that name already exists!");

    var recipeToCreate = _autoMapper.Map < Recipe > (recipeForCreateDto);

    recipeToCreate.AppUserId = userFromRepo.Id;

    var createdRecipe = await _recipeRepository.AddNewRecipe(recipeToCreate); // here is problem 
    var recipeToReturn = _autoMapper.Map < RecipeForDetailDto > (createdRecipe);

    return CreatedAtRoute("GetRecipe", new {
            controller = "Recipes",
            id = createdRecipe.Id
        },
        recipeToReturn);
}

Answer 2

请务必注意，.Net 中的 默认序列化程序 现在来自 System.Text.Json.Serialization 命名空间。这个序列化程序实际上在序列化和反序列化循环引用方面做得很好。

要启用此功能，请将以下代码放入您的 Startup.cs：

services
   .AddControllers()
   .AddJsonOptions(c => c.JsonSerializerOptions.ReferenceHandler = ReferenceHandler.Preserve);

在此处记录：https://docs.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-preserve-references

Answer 3

“检测到可能的对象循环。这可能是由于 循环或如果对象深度大于最大允许深度 32. 考虑使用 ReferenceHandler.Preserve 支持循环的 JsonSerializerOptions。"

对于这个问题，可以在startup.csConfigureServices方法中添加如下代码：

services.AddControllersWithViews()
    .AddNewtonsoftJson(options =>
    options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
);